The present invention relates to the field of electrical connectors, particularly connectors for coaxial cables. The preferred connectors are particularly well suited for use in harsh environments wherein it is desirable to seal the connection from the elements. One such application is in data transmission systems for downhole environments, such as along a drill string used in oil and gas exploration or along the casings and other equipment used in oil and gas production. The goal of accessing data from a drill string has been expressed for more than half a century. As exploration and drilling technology has improved, this goal has become more important in the industry for successful oil, gas, and geothermal well exploration and production. For example, to take advantage of the several advances in the design of various tools and techniques for oil and gas exploration, it would be beneficial to have real time data such as temperature, pressure, inclination, salinity, etc. Several attempts have been made to devise a successful system for accessing such drill string data. One such system is disclosed in co-pending U.S. application Ser. No. 09/909,469 (also published as PCT Application WO 02/06716) which is assigned to the same assignee as the present invention. The disclosure of this U.S. Application Serial No. 09/909469 is incorporated herein by reference.
Briefly stated, the invention is a system for retainging an electrical transmission line through a string of downhole components.
In accordance with one aspect of the invention, the system includes a plurality of downhole components, such as sections of pipe in a drill string. Each component has a first and second end, with a first communication element located at the first end and a second communication element located at the second end. Each communication element includes a first contact and a second contact. The system also includes a coaxial cable running between the first and second communication elements, the coaxial cable having a conductive tube and a conductive core within it. The system also includes a first and second connector for connecting the first and second communication elements respectively to the coaxial cable. Each connector includes a conductive sleeve, lying concentrically within the conductive tube, which fits around and makes electrical contact with the conductive core. The conductive sleeve is electrically isolated from the conductive tube. The conductive sleeve of the first connector is in electrical contact with the first contact of the first communication element, the conductive sleeve of the second connector is in electrical contact with the first contact of the second communication element, and the conductive tube is in electrical contact with both the second contact of the first communication element and the second contact of the second communication element.
The first and second communication elements are preferably inductive coils, and the inductive coils are preferably formed by a single loop of wire. More preferably, the inductive coils include at least one loop of wire set in circular trough of a magnetically conducting, electrically insulating material, preferably ferrite. Preferably, the trough is formed of segments of a magnetically conducting electrically insulating material, with the electrically insulating material segments preferably retained within a groove formed in a metal ring.
In accordance with another aspect of the invention, the components are sections of drill pipe, each having a central bore, and the first and second communication elements are located in a first and second recess respectively at each end of the drill pipe. The system further includes a first passage passing between the first recess and the central bore and a second passage passing between the second recess and the central bore. The first and second connectors are located in the first and second passages respectively. Preferably, each section of drill pipe has a portion with an increased wall thickness at both the box end and the pin end with a resultant smaller diameter of the central bore at the box end and pin end, and the first and second passages run through the portions with an increased wall thickness and generally parallel to the longitudinal axis of the drill pipe. The box end and pin end is also sometimes referred to as the box end tool joint and pin end tool joint.
In accordance with another aspect of the invention, the system includes a first and second expansion plug, each of which includes a central passage and each of which is press-fit within the conductive tube so as to maintain the increased outside diameter of the conductive tube within the larger diameter portions of the first and second passages respectively. The system also preferably includes a first and second retaining plug, each of which includes ridges on its outer surface to retain the expansion plugs in place.
The expansion plugs could alternatively be internal diametrical expansion mandrels with a central passage, the expansion mandrel having a front and back end. The back end of the expansion mandrel has an outer diameter that is greater than an outer diameter of the front end of the expansion mandrel. The retention plugs could alternatively be expansion mandrels with the back end having external circumferential grooved barbs, also known as a barbed expansion mandrel, that dig into the conductive tube internal diameter. These expansion mandrels become electrical transmission line retainers when displaced within and electrical transmission line. The central passage of the expansion mandrels or retainers could also be electrically insulated allowing bare wire to pass through without causing an electrical short.
In accordance with another aspect of the invention, the first and second communication elements each includes an inductive coil having at least one loop of wire. In each communication element, there is a water-tight seal between the wire and the inside of the conductive tube. The water-tight seal preferably includes at least one gasket through which the first end of the wire passes and which forms a seal with the inner surface of the conductive tube.
The invention also includes a method of electrically connecting communication elements at opposite ends of a downhole component through a coaxial conductor. The method includes providing a coaxial cable as the conductor between the first and second communication elements. The coaxial cable includes a conductive tube, a conductive core within the conductive tube and a dielectric material between the conductive tube and the conductive tube. The method also includes providing a first and second connector for connecting the first and second respective communication elements to the coaxial cable. The first and second connectors each include a conductive sleeve that fits around and makes electrical contact with the conductive core. The conductive sleeve is electrically isolated from the conductive tube. The method also includes removing a portion of the dielectric material at both ends of the coaxial cable to provide clearance for the conductive sleeve, and sliding the first and second connectors over both ends of the coaxial cable.
In accordance with another aspect of the invention, the method includes expanding the outside diameter of the conductive tube by inserting an expansion plug or mandrel into each end. The first and second communication elements each include an inductive coil having at least one loop of wire. In each communication element, a first end of the wire is in electrical contact with the conductive tube and a second end of the wire is in electrical contact with the conductive sleeve. The method further includes inserting a water-tight seal between the second end of the wire and the inside of the conductive tube.
The present invention, together with attendant objects and advantages, will be best understood with reference to the detailed description below in connection with the attached drawings.